This application claims the benefit of Korean patent application number P2000-0866, filed Feb. 23, 2000 which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
This invention relates to an apparatus for mounting an integrated circuit in a liquid crystal display, and more particularly to a tape carrier package that reduces the possibility of a short between adjacent pads when bonding the tape carrier package to a liquid crystal panel and/or a printed wiring substrate. Also, the present invention is related to a method of fabricating such a tape carrier package.
2. Description of the Related Art
Generally, an active matrix liquid crystal display uses thin film transistors (TFTs) as switching devices to display natural-looking moving pictures. Since such a liquid crystal display can be made into a smaller-size device than a cathode ray tube, it is commercially viable for use a monitor such as a portable television, lap-top personal computer or other consumer device.
The active matrix liquid crystal display displays a picture corresponding to video signals such as television signals on a pixel (or picture element) matrix having pixels arranged at each intersection between gate lines and data lines. Each pixel includes a liquid crystal cell for controlling a transmitted light quantity in accordance with a voltage level of a data signal from a data line. A TFT (thin film transistor) is installed at an intersection between a gate line and a data line to switch a data signal to be transferred to the liquid crystal cell in response to a scanning signal (i.e., a gate pulse) from the gate line.
Such a liquid crystal display requires a number of integrated circuits (ICs) connected to the data lines and the gate lines to apply data signals and scanning signals to the data lines and the gate lines, respectively. The ICs are installed between the print wiring board (PWB) and the liquid crystal panel to apply signals supplied from the PWB to the data lines and the gate lines. IC mounting methods include chip on board, hereinafter referred to as xe2x80x9cCOBxe2x80x9d, tape automated bonding, hereinafter referred to as xe2x80x9cTABxe2x80x9d, and a chip on glass, hereinafter referred to as xe2x80x9cCOGxe2x80x9d. (Other methods are also possible). The COB system is mainly used for monochromatic liquid crystal displays having a pixel pitch of more than 300 xcexcm. As shown in FIG. 1, in this COB system, ICs 8 are mounted on a PWB 6 and a heat-seal connector 10 connects the PWB 6 and a glass substrate 3 in a liquid crystal panel 2. In this case, a back light unit 4 used as a light source is provided between the liquid crystal panel 2 and the PWB 6. As shown in FIG. 2, in the TAB system, ICs 14 are mounted on a tape carrier package (TCP) 12. The TCP 12 is connected between the PWB 6 and the liquid crystal panel 3. As shown in FIG. 3, in the COG system, an IC chip 20 is directly mounted on a glass substrate 17 in a liquid crystal panel 16.
The above-mentioned TAB IC mounting method has been widely employed because it can widen an effective area of the panel and has a relatively simple mounting process.
As shown in FIG. 4, the TCP 12 employed in the TAB system includes a base film 22 on which is mounted an IC 14. The base film 22 is also provided with input and output pads 24 and 26 connected to input and output pins of the IC 14. The input and output pads 24 and 26 have a two-layer structure in which copper(Cu) is plated with tin(Sn) for preventing oxidation. Line widths of the input pads 24 are set to be larger than those of the output pads 26. As shown in FIG. 5, the input pads 24 of the base film 22 are connected, via an anisotropic conductive film (ACF) 30, to pads 28 on the PWB 6. The output pads 26 are also connected via the ACF 30 to pads 28 on the liquid crystal panel 2.
However, the IC mounting method employing the TAB system has a problem in that a conductive alien substance produced from a cutting process of TCP 12 may generate a short between the pads 28 on the liquid crystal panel 2 or the PWB 6 and the pads 24 and 26 of the base film 22, respectively as shown in FIG. 5. More specifically, the TCP 12 is formed on a flexible polyimide film roll (FPFR) 32 and then is cut into the shape shown by the dashed line 40 in FIG. 6. In this case, the input and output pads 24 and 26 extend outside of a cutting line 40. At this time, as seen from FIG. 7A and FIG. 7B, the input pads 24 have the same line width at the inside and outside of the cutting line 40. The output pads 24 also have the same line width inside and outside of the cutting line 40. In FIG. 7A and FIG. 7B, a bonding layer 27 functions to adhere the input and output pads 24 and 26 on the base film 22. An extension of the input and output pads 24 and 26 into a dummy area outside of the cutting line 40 aims at electrically testing whether or not there is a defect in the IC 14, the pads 24, 26 and/or the interconnection pattern between the IC 14 and the pads 24, 26, before the base film 22 has been cut. After the test, the base film 22 and the input and output pads 24 and 26 are cut along the cutting line 40. At this time, a portion of the input and output pads 24 and 26 on the cutting line 40 may come off due to friction between a cutter (not shown) and the input and output pads 24 and 26. A conductive alien substance 42 generated in this manner is adhered to the TCP 12 by static electricity such that the material 42 is loaded into a pad bonding equipment (not shown) along with the TCP 12. This conductive alien substance 42 is interposed between the pads 28 of the PWB 6 or the liquid crystal panel 2 and the input and output pads 24 and 26 as shown in FIG. 5 during the pad bonding process, which causes an insulation breakdown of the ACF 30. As a result, the pads 28 on the adjacent PWB 6 or liquid crystal panel 2 and/or the input and output pads 24, 26 are short-circuited due to the conductive alien substance 42. Particularly, as line widths of the input and output pads 24 and 26 on the cutting line 40 are relatively wide, so too is the size of the conductive alien substance 42. Since a distance between panels in a high-resolution liquid crystal display is narrow, a conductive alien substance 42 with a small size also may cause a short between panels in such a high-resolution liquid crystal display.
Accordingly, it is an object of the present invention to provide a tape carrier package that reduces the possibility of a short between adjacent pads.
A further object of the present invention is to provide a method of fabricating a tape carrier package that reduces the possibility of a short between adjacent pads.
In order to achieve these and other objects of the invention, a tape carrier package according to one aspect of the present invention includes a base film for mounting an integrated circuit; input pads connected to the integrated circuit and output pads connected to the integrated circuit, each of the output pads including a first portion adjacent to the integrated circuit and a second portion extended from the first portion, wherein the second portion has a narrower line width than the first portion.
A method of fabricating a tape carrier package according to another aspect of the present invention includes the steps of forming input pads at the inside of a coating line of the tape carrier package on a base film; forming output pads including a first portion connected to an integrated circuit on the base film, a second portion positioned at the cutting line and having a narrower line with than the first portion, and a third portion extending from the second portion and having a wider line width than the second portion; mounting the integrated circuit on the base film; connecting the input pads and the first portions; to the integrated circuit and the base film along the cutting line.